DIY origami fish tutorial, paper folding, paper craft Easiest Orgami Fish directions I could find. Plan B if the pool party gets rained out.
Science project: 2 clear containers, water, shaving cream, food coloring, and droppers. Slowly pour the food coloring on top of the shaving cream clouds and watch the "rain" come down when the clouds get saturated.
Second Grade Construction & Sculpture Activities: Octopus Mobile
The Water Cycle activity
Easy and cute kids
Stuff and Spill Picnic Basket
How to make popsicle turtles using three sticks and God's Eye Weaving Pattern. While this is a great art project, it's good as a busy hands/ meditation activity as well
Making a small aquarium. You can use a letter box, shoe box lid, etc.